The present invention relates to a technology for improving the recording performance of a magnetic disk device, and more particularly, to a technology for achieving stable recording performance, even if the clearance between a head and a recording disk varies with a temperature change.
The magnetic head used for a magnetic disk device is formed (using a thin-film process) at the end of a slider constructed of a sintered body consisting of aluminum (Al), titanium (Ti), and carbon (C), called AlTiC. Hereinafter, a combination of the magnetic head and the slider is referred to collectively as the head/slider. An air-bearing surface (ABS) is formed on the surface of the head/slider that faces the magnetic disk. When the viscous air stream generated on the surface of the magnetic disk which rotates flows along the ABS and the surface of the magnetic disk, the ABS undergoes buoyant force and lifts the head/slider from the surface of the magnetic disk to a position at which the buoyant force maintains a balance with respect to the pressure load of the head gimbal assembly supporting the slider. As a result, while the magnetic disk is rotating, a clearance of a required range is maintained between the magnetic head and a magnetic layer thereof. In order for the magnetic head to perform stable read/write operations on the magnetic layer, the clearance between the magnetic head and the magnetic layer needs to be maintained in the required range.
Too small a clearance between the magnetic head and the magnetic layer could bring the head/slider into contact with the surface of the magnetic disk, resulting in the magnetic disk and the magnetic head being damaged. Conversely, too great a clearance weakens magnetic coupling between the magnetic head and the magnetic layer, thus leading to unstable data read/write operations. In general, the magnetic head is formed up of an inductive recording head which has coils, magnetic pole pieces, and recording gaps, and a giant magnetoresistive (GMR) head which uses GMR elements, or a magnetoresistive (MR) head which uses MR elements.
When a recording current is supplied to the recording head in order to write data onto the magnetic disk, the resistance existing in the coils of the recording head generates heat and increases the peripheral temperatures of the coils. At this time, any differences in thermal expansion coefficient, between the materials constituting the recording head and the materials constituting the slider body, will cause the event, called thermal protrusion, that the sections where the magnetic pole pieces of the recording head form the recording gaps protrude from the ABS. Even if the clearance between the head/slider and the magnetic disk surface is constant, such thermal protrusion will change the clearance between the recording head and the magnetic layer, resulting in trouble with the recording operation.
Patent Document 1 (Japanese Patent Laid-Open No. 2004-110918) discloses a technology for suppressing the deterioration of recording performance, coupled with the contraction of the head elements under a low-temperature environment after the start of recording. According to the invention described in this Patent Document, dummy data is recorded on dummy tracks of a medium for a time interval immediately before desired data is recorded. Patent Document 2 (Japanese Patent Laid-Open No. 2004-79126) discloses a technology for preventing the occurrence of errors by retracting the recessed section of a magnetic head at low temperature and thus increasing a magnetic spacing. According to the invention described in this Patent Reference, before data is recorded, the internal temperature of a magnetic disk device is detected, then its magnetic head is moved to a non-recording region, and at least one sector of dummy data is recorded. Patent Document 3 (Japanese Patent Laid-Open No. 2002-237004) discloses a technology by which the setting of the writing current to be used is changed according to ambient temperature.